Method and device for activating secondary carrier in wireless communication system for using carrier aggregation technique

ABSTRACT

The present invention proposes a method for activating secondary carriers in addition to the primary carrier in a wireless communication system supporting carrier aggregation technology. Through the present invention, the UE sorts the operations for activating an SCell into two groups that are executed at different timings, thereby facilitating communication without malfunctioning.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system and, inparticular, to a method for activating a secondary carrier in additionto the primary carrier in a Long Term Evolution (LTE) system supportingCarrier Aggregation.

2. Description of the Related Art

With the rapid advance of wireless communication technology, thecommunication system has evolved to the 4^(th) Generation mobilecommunication systems such as Long Term Evolution (LTE) system. The LTEsystem adopts various techniques to meet the increased trafficrequirements and, Carrier Aggregation is one of these techniques. Thecarrier aggregation is a technique capable of increasing the data ratein proportion to the number of aggregated carriers including pluralsecondary carrier as well as the primary carrier between a UserEquipment (UE) and an evolved Node B (eNB) as compared to theconventional system using a single carrier. In LTE, the primary cell isreferred to as PCell and the secondary cell is referred to as SCell.

In order to use the carrier aggregation technique, it is inevitable thatthe complexity increases to control the PCell and the SCells. That is,there is a need of control to determine the SCell(s) to be configuredfor use along the PCell and to be activated for actual use.

There is therefore a need of a detailed procedure for activating anSCell. That is, it is necessary to specify the operation of the UE whenan SCell activation command is received from the eNB.

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made in an effort to solve the aboveproblem, and it is an object of the present invention to provide amethod for activating secondary carriers in the mobile communicationsystem supporting carrier aggregation.

Solution to Problem

In the present invention, the operations for performing secondarycarrier (SCell) activation are sorted into two groups that are executedat different timings.

In order to accomplish this, a secondary carrier activation method of aterminal in a wireless communication system supporting carrieraggregation includes receiving secondary carrier aggregation activationinformation instructing activation of secondary carriers configured tothe terminal; checking a first timing in configuring the activation ofthe secondary carriers and performing first operations at the firsttiming; and checking a second timing and performing second operationsbefore the second timing.

A terminal for activating secondary carriers under the control of a basestation in a wireless communication system supporting carrieraggregation includes a transceiver which transmits and receives controlsignals or data to and from the base station; and a controller whichcontrols receiving secondary carrier aggregation activation informationinstructing activation of secondary carriers configured to the terminalfrom the base station, checking a first timing in configuring theactivation of the secondary carriers and performing first operations atthe first timing, and checking a second timing and performing secondoperations before the second timing.

Advantageous effects

With the proposed method, it is possible to execute all the operationsfor activating cells such that the UE is capable of performing thesecondary carrier activation without error.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the architecture of an LTE system towhich the present invention is applied;

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied;

FIG. 3 is a diagram illustrating an exemplary situation of carrieraggregation in the LTE system to which the present invention is applied;

FIG. 4 is a signaling diagram illustrating message flows between the eNBand the UE in the secondary carrier activation method according to anembodiment of the present invention;

FIG. 5 is a diagram illustrating operation timings in unit of subframefor secondary carrier activation method according to an embodiment ofthe present invention;

FIG. 6 is a flowchart illustrating the UE procedure of the SCellactivation method according to an embodiment of the present invention;

FIG. 7 is a flowchart illustrating the eNB procedure of the SCellactivation method according to an embodiment of the present invention;and

FIG. 8 is a block diagram illustrating the configuration of the UEaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following, detailed description of well-known functions andstructures incorporated herein may be omitted to avoid obscuring thesubject matter of the present invention. Exemplary embodiments of thepresent invention are described with reference to the accompanyingdrawings in detail.

The present invention relates to a secondary carrier activation methodand apparatus of a UE capable of carrier aggregation.

FIG. 1 is a diagram illustrating the architecture of an LTE system towhich the present invention is applied.

Referring to FIG. 1, the radio access network of the mobilecommunication system includes evolved Node Bs (eNBs) 105, 110, 115, and120, a Mobility Management Entity (MME) 125, and a Serving-Gateway(S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135connects to an external network via eNBs 105, 110, 115, and 120 and theS-GW 130.

In FIG. 1, the eNBs 105, 110, 115, and 120 correspond to legacy node Bsof Universal Mobile Communications System (UMTS). The eNBs 105, 110,115, and 120 allow the UE to establish a radio link and are responsiblefor complicated functions as compared to the legacy node B. In the LTEsystem, all the user traffic including real time services such as Voiceover Internet Protocol (VoIP) are provided through a shared channel andthus there is a need of a device which is located in the eNB to scheduledata based on the state information such as UE buffer conditions, powerheadroom state, and channel state. Typically, one eNB controls aplurality of cells. In order to secure the data rate of up to 100 Mbps,the LTE system adopts Orthogonal Frequency Division Multiplexing (OFDM)as a radio access technology. Also, the LTE system adopts AdaptiveModulation and Coding (AMC) to determine the modulation scheme andchannel coding rate in adaptation to the channel condition of the UE.The S-GW 130 is an entity to provide data bearers so as to establish andrelease data bearers under the control of the MME 125. MME 125 isresponsible for various control functions and connected to a pluralityof eNBs 105, 110, 115, and 120.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control(RLC) 210 and 235, Medium Access Control (MAC) 215 and 230, and Physical(PHY) 220 and 225. The PDCP 205 and 240 is responsible for IP headercompression/decompression, and the RLC 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation. ARQ isthe technique for checking whether the packet transmitted by thetransmitted is received by the received successfully and retransmittingthe packets received erroneously. The MAC 215 and 230 is responsible forestablishing connection to a plurality of RLC entities so as tomultiplex the RLC PDUs into MAC PDUs and demultiplex the MAC PDUs intoRLC PDUs. The PHY 220 and 225 performs channel coding on the MAC PDU andmodulates the MAC PDU into OFDM symbols to transmit over radio channelor performs demodulating and channel-decoding on the received OFDMsymbols and delivers the decoded data to the higher layer.

FIG. 3 is a diagram illustrating an exemplary situation of carrieraggregation in the LTE system to which the present invention is applied.

Referring to FIG. 3, typically an eNB can use multiple carrierstransmitted and receive in different frequency bands. For example, theeNB 305 can be configured to use the carrier 315 with center frequencyf1 and the carrier 310 with center frequency f3. If carrier aggregationis not supported, the UE 330 has to transmit/receive data unit one ofthe carriers 310 and 315. However, the UE 330 having the carrieraggregation capability can transmit/receive data using both the carriers310 and 315. The eNB can increase the amount of the resource to beallocated to the UE capable of carrier aggregation in adaptation to thechannel condition of the UE so as to improve the data rate of the UE.

In case that a cell is configured with one downlink carrier and oneuplink carrier as a conventional concept, the carrier aggregation can beunderstood as if the UE communicates data via multiple cells. With theuse of carrier aggregation, the maximum data rate increases inproportion to the number of aggregated carriers.

In the following description, the phrase “the UE receives data through acertain downlink carrier or transmits data through a certain uplinkcarrier” means to transmit or receive data through control and datachannels provided in a cell corresponding to center frequencies andfrequency bands of the downlink and uplink carriers. Although thedescription is directed to an LTE mobile communication system forexplanation convenience, the present invention can be applied to othertypes of wireless communication systems supporting carrier aggregation.

An embodiment of the present invention proposes a UE operation when asecondary carrier (SCell) activation command is received from the eNB.In an embodiment of the present invention, the UE operations uponreceipt the secondary carrier activation command are sorted into twosets which are applied at different timings. This is because if theoperations requiring different operation time durations are executed atthe same timing determined based on the operation requiring longer timeduration this increases the activation delay.

For example, the UE cannot use the secondary carrier (SCell) for datatransmission upon receipt of the command from the eNB. This is becauseit takes addition time to activate devices for use of the secondarycarrier (SCell). Furthermore, once the devices have been activated,there may be other operations requiring more time.

FIG. 4 is a signaling diagram illustrating message flows between the eNBand the UE in the secondary carrier activation method according to anembodiment of the present invention.

The eNB 403 determines the SCells to be activated or deactivated amongthe SCells configured to the UE 401. The eNB generates a SCellactivation information (or Activation/Deactivation MAC Control Element(CE) including an indicator indicating activation or deactivation of theSCell and sends the UE 401 the Activation/Deactivation MAC CE at N^(th)subframe at step 405. The Activation/Deactivation MAC CE is 8-bit fixedsize MAC CE including 7 C fields and one R field. Here, R denotes areserved field, and 7 C fields are expressed as C7, C6, C5, C4, C3, C2,and C1 (i.e. Ci). If Ci corresponding to SCell i is set to 1, thisindicates activation and, otherwise if Ci is set to 0, this indicatesdeactivation.

If the Activation/Deactivation MAC CE is received, the UE checks theSCells to be activated or deactivated at step 407 and checks the firsttiming at step 409. The first timing is (N+m)^(th) subframe where m is ainteger equal to or greater than 1 (e.g. 8). The first timing is ofperforming the operations that can be executed immediately among theUE's SCell activation operations. The parameter m is preferably set to avalue large enough by taking notice of the UE having low processingcapability in consideration of the time necessary for the UE to receiveand decode the Activation/Deactivation MAC CE and recognize the meaning.

At the first timing of (N+m)^(th) subframe, the UE 401 performs thepredetermined first operations at step 411. The first operations are asfollows.

-   -   scheduling channel monitoring    -   CQI measurement    -   PUSCH transmission/PDSCH reception    -   CQI reporting    -   SRS transmission

Afterward, the UE 401 checks the second timing at step 413. The secondtiming (N+z+4)^(th) subframe where z is an integer equal to or greaterthan m, (N+z)th subframe is the downlink subframe available for channelquality (Channel Quality Information (CQI) or Channel Status Information(CSI)) measurement which arrives first, and 4 is a constant value givenfor measurement before 4 subframes. That is, the CQI measurement isperformed at (N+z)^(th) subframe, and the measured CQI is reported atthe (N+z+4)^(th) subframe or later. The valid downlink subframe isdefined as the time fulfilling the following conditions:

-   -   DL subframe is configured for corresponding UE,    -   transmission mode 9 is ruled out and no MBSFN subframe,    -   not include DwPTS field when the length of DwPTS is equal to or        less than 7680*TS    -   the subframe is not positioned in measurement gap for the UE    -   For periodic CSI report, CSI subframe set is configured to the        UE, component of CSI subframe associated with periodic CSI        report.

After checking the second timing, the UE 401 performs the predeterminedsecond operations before the second timing. Here, the predeterminedsecond operations include the operations related to CQI report asfollows.

-   -   If valid CQI measurement is performed, report CQI actually.    -   At the CQI reporting timing, the UE reports a CQI index value        selected in the range from 1 to 15 by referencing table 1        according to the actual measurement.

TABLE 1 CQI index modulation code rate × 1024 efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 12 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

-   -   if there is no valid CQI, report CQI set to 0 (refer to table        1).

Next, the UE reports the CQI before the second timing at step 417 suchthat all the operations are performed correctly since the second timing.

FIG. 5 is a diagram illustrating operation timings in unit of subframefor secondary carrier activation method according to an embodiment ofthe present invention.

In FIG. 5, the CQI report resource for SCell is allocated at an intervalof 5 ms (a subframe has a length of 1 ms) and indicated by arrows (at[n−7], [n−2], [n+3], [n+8], . . . ).

First, the UE receives the Activation/Deactivation MAC CE at (n−5)^(th)subframe. At this time, the UE interprets the MAC CE to determine theSCells to be activated or deactivated for a certain time. Assuming thatit takes 6 msec for activation/deactivation of the synchronized SCells,the value m is 6 at the first timing in FIG. 4. At [n+1] of FIG. 5, theUE performs the first operations scheduled to be performed at the firsttiming, and this is identical with the description of step 411 of FIG.4.

Here, the first timing is the last time point when the operationsscheduled to be performed at the first timing are initiated, and if theUE is capable of interpreting the MAC CE as soon as possible, theoperations can be performed in advance. In this case, the next CQIreport can be performed with the average of more values so as to reportmore accurate value.

Afterward, the UE calculates the second timing of FIG. 4 (after 4subframes in FIG. 5) and starts the second operations scheduled to beperformed at the second timing. The CQI report is performed as describedwith reference to FIG. 4, and the UE starts CQI report for the SCellbased on the second timing. That is, although the resource for CQIreport is allocated at [n−7], [n−2], and [n+3] timings in FIG. 5, theCQI report is not performed at these timings but at [n+8] timing as thefirst resource allocated since the subframe [n+5]. Here, comparing the[n+5] timing of FIG. 5 to (N+z+4) defined as the second timing in FIG.4, z equal to m, i.e. 6. If the UE has the capability of reporting CQIbefore the second timing, it is possible to report the CQI before thesecond timing.

FIG. 6 is a flowchart illustrating the UE procedure of the SCellactivation method according to an embodiment of the present invention.

First, the UE receives the Activation/Deactivation MAC CE including an8-bit bitmap at the N^(th) at step 601. Each bit of the bitmap carriedin the MAC CE indicates whether to activate/deactivate the correspondingSCell.

If the Activation/Deactivation MAC CE is received, the UE determineswhether there is any SCell to be newly activated and, if so, checks theSCell to be activated at step 603. In more detail, the UE checks thedeactivated SCells before the receipt of the MAC CE and, when the MAC CEis received, determines whether any of the deactivated SCells isindicated to be indicated to be activated by the corresponding bit ofthe bitmap in the MAC CE.

If any SCell to be activated newly is checked, the UE checks the firsttiming and performs the operations scheduled to be performed at thefirst timing at step 605. The first timing corresponds to (N+m)^(th)subframe, i.e. the subframe arriving after m subframes since the receiptof the Activation/Deactivation MAC CE at N^(th) subframe. The UEperforms the first operation scheduled to be performed at the firsttiming based on the (N+m)^(th) subframe. As described with reference toFIG. 4, these operations include at least one of the followingoperations that have been described with reference to FIG. 4.

-   -   scheduling channel monitoring    -   CQI measurement    -   PUSCH transmission/PDSCH reception    -   CQI reporting    -   SRS transmission

Also, m is the fixed value known to all UEs and eNBs (e.g. m=8).

Afterward, the UE checks the second timing and performs the secondoperations scheduled to be performed at the second timing at step 607.The second timing is the (N+z+4)th subframe equal to the second timingof FIG. 4, and z is an integer value equal to or greater than m. Thesecond operations scheduled to be performed at the second timingincludes CQI report as described with reference to FIG. 4. In moredetail, the UE reports the CQI for the activated SCell through theallocated CQI report resource arriving first since the second timing.The UE also reports the CQI for the SCell continuously through the CQIreport resource allocated for the activated SCell. Although the CQIreport is not transmitted between the first and second timings, if thevalid CQI measurement result becomes available before the arrival of thesecond timing, it is possible to perform CQI report for the SCell. Ifthere is no valid CQI measurement result between the first and secondtimings, the UE reports a predetermined value (e.g. CQI=0). However, ifvalid CQI measurement result is achieved before the second timing, theUE stops reporting the predetermined value and reports the report valuereflecting the actual CQI measurement result to the eNB.

FIG. 7 is a flowchart illustrating the eNB procedure of the SCellactivation method according to an embodiment of the present invention.

The eNB determines whether to activate SCell x of the UE at step 701.This may be the case when the traffic load of the cell increases due tothe increase of the number of UEs served by the eNB.

Afterward, the eNB generates and transmits Activation/Deactivation MACCE message for activating the SCell x at step 703.

Afterward, the eNB performs the first operations scheduled to beperformed at the first timing at step 405. The first operations includeallocating resource to the UE in the SCell x and receiving signals suchas SRS message.

Finally, the eNB performs the operations scheduled to be performed atthe second timing at step 407. These operations include receiving theCQI report at the subframe designated to carry the CQI report of theSCell.

FIG. 8 is a block diagram illustrating the configuration of the UEaccording to an embodiment of the present invention.

The UE communicates data with higher layer processor 805 andtransmits/receives control messages via the control message processor807. When transmitting control signal or data to the eNB, the UEmultiplexes the control signals or data by means of themultiplexer/demultiplexer 803 and transmits the multiplexed signals toby means of the transceiver 801 under the control of the controller 809.The UE also receives the physical signal by means of the transceiver801, demultiplexes the received signal by means of themultiplexer/demultiplexer 803, and delivers the demultiplexedinformation to the higher layer processor 805 or control messageprocessor 807 under the control of the controller 809.

In an embodiment of the present invention, if theActivation/Deactivation MAC CE is received, the control messageprocessor 807 notifies the SCell activation processor 811 of the receiptof the Activation/Deactivation MAC CE. The SCell deactivation processor811 checks the first timing and instructs the controller 809 and thecontrol message processor 807 to perform the first operations at thefirst timing or even before the arrival of the first timing. Afterward,the SCell activation processor 811 checks the second timing and performsthe second operations at the second timing or even before the arrival ofthe second timing. The second operations include reporting CQI for thesecond cell, and the CQI report for the SCell is performed using the CQIreport resource allocated for the SCell.

Although FIG. 8 is directed to the case where the UE is configured withplural function blocks in charge of different roles, the presentinvention is no limited thereto. For example, the functions of the SCellactivation processor 811 can be performed by the controller 809.

As described above, the SCell activation method of the present inventionis capable of facilitating execution of the operations scheduled to beperformed at predetermined timings in activating an SCell, resulting inimprovement operation reliability.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove with specific terminology, this is forthe purpose of describing particular embodiments only and not intendedto be limiting of the invention. While particular embodiments of thepresent invention have been illustrated and described, it would beobvious to those skilled in the art that various other changes andmodifications can be made without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A secondary carrier activation method of aterminal in a wireless communication system supporting carrieraggregation, the method comprising: receiving secondary carrieraggregation activation information instructing activation of secondarycarriers configured to the terminal; checking a first timing inconfiguring the activation of the secondary carriers and performingfirst operations at the first timing; and checking a second timing andperforming second operations before the second timing.
 2. The method ofclaim 1, wherein the first timing is (N+m)^(th) subframe where N denotesa subframe carrying the secondary carrier activation information and mis an integer equal to or greater than
 1. 3. The method of claim 2,wherein the first operations comprise at lease on of scheduling channelmonitoring, channel quality information measurement, uplink or downlinkdata transmission/reception, channel quality information report, andsounding reference signal transmission.
 4. The method of claim 3,wherein the second timing is (N+z+4)^(th) subframe where N denotes thesubframe carrying the secondary carrier activation information and z isan integer equal to or greater than m.
 5. The method of claim 4, whereinthe second operations comprises reporting channel measurementinformation.
 6. A terminal for activating secondary carriers under thecontrol of a base station in a wireless communication system supportingcarrier aggregation, the terminal comprising: a transceiver whichtransmits and receives control signals or data to and from the basestation; and a controller which controls receiving secondary carrieraggregation activation information instructing activation of secondarycarriers configured to the terminal from the base station, checking afirst timing in configuring the activation of the secondary carriers andperforming first operations at the first timing, and checking a secondtiming and performing second operations before the second timing.
 7. Theterminal of claim 6, wherein the first timing is (N+m)^(th) subframewhere N denotes a subframe carrying the secondary carrier activationinformation and m is an integer equal to or greater than
 1. 8. Theterminal of claim 7, wherein the first operations comprise at lease onof scheduling channel monitoring, channel quality informationmeasurement, uplink or downlink data transmission/reception, channelquality information report, and sounding reference signal transmission.9. The terminal of claim 8, wherein the second timing is (N+z+4)^(th)subframe where N denotes the subframe carrying the secondary carrieractivation information and z is an integer equal to or greater than m.10. The terminal of claim 9, wherein the second operations comprisesreporting channel measurement information.